Four Liberals seek Senate president post

Veteran Nationals senator John 'Wacka' Williams has withdrawn from the race to be Senate president, leaving it as a five-way contest.

It is understood Special Minister of State Scott Ryan and backbenchers Dean Smith, Ian Macdonald and David Fawcett will throw their hats in the ring at a meeting of Liberal senators in Canberra on Monday morning.

A ballot of all senators will be needed on Monday, as Greens senator Peter Whish-Wilson also plans to nominate - pledging to donate the extra pay to charity.